Method of applying polyarylene sulphide compositions to a bearing

ABSTRACT

A method of applying a coating of polyarylene sulphide to a bearing in which an initmate mixture of a polyarylene sulphide with an aryl ester of an aryl alcohol is applied to a bearing blank and subsequently heated to evaporate the ester and cure the coating. The mixture can be a dry powder mixture, a wet powder mixture, a paste, a suspension, a liquid solution or a solid solution. The preferred mixture comprises polyphenylene sulphide and benzyl benzoate.

The present invention relates to a method of applying polyarylenesulphide compositions to a bearing.

Polyarylene sulphides have properties which make them suitable for usein various situations, for example as plain bearing linings. However,they also possess properties which make their preparation andapplication inconvenient and frequently difficult.

Available techniques involve the use of toxic chemicals or techniquesinvolving what is essentially powder fusion. The powder fusiontechniques limit the roles in which polyarylene sulphides can be usedand involve slow processes of low productivity.

One of the properties of polyarylene sulphides which limits their use istheir high viscosities in the molten state. This renders thedistribution of the material difficult in the extreme and makes itdifficult therefore to establish a bond between the polyarylene sulphideand another material. One known method of forming a bond between thepolyarylene sulphide and another material is to apply the polyarylenesulphide powder to the other material as level and evenly as possible,and then to melt, cure and cross-link the powder. Water baseddispersions of PPS are also known but this is just another form ofapplying powder since this is what remains after the water has beenevaporated.

However, as stated above, using polyarylene sulphide powder involvesconsiderable manufacturing difficulties. Polyphenylene sulphide takes along time to cure and crosslink particularly when the powder layer isrelatively thick. Also since the molten powder has a high viscosity andgenerally does not flow or wet a surface very well, this results invoids and consequently a poor bond between the polyphenylene sulphideand the other material which bond may fail when under load.

It is also difficult to achieve a precision thickness of polyarylenesulphide which is dimensionally stable and even more difficult toproduce a very thin, cured layer.

It is an object of the present invention to provide a method of applyingpolyarylene sulphide in a workable form in order to minimise the abovedifficulties in providing a plain bearing having a coating ofpolyphenylene sulphide.

The present invention is based on the discovery that benzyl benzoate hasa plasticizing and, in sufficient quantities, a solvent action onpolyphenylene sulphide.

According to the present invention a method of applying a coating ofpolyarylene sulphide to a bearing is characterised by applying a mixtureof polyarylene sulphide and an aryl ester of an aryl alcohol to thesurface of a bearing blank, and subsequently heating the mixture toevaporate the ester and to cure the coating.

The mixture may be a two phase mixture of resin or a resin rich phasecomprising polyarylene sulphide and a solvent or a solvent rich phasecomprising an aryl ester of an aryl alcohol preferably benzyl benzoate.Alternatively, the mixture may be a single phase mixture of the resin insolution in the solvent or vice versa.

The resin phase may further include other resins besides polyarylenesulphide in either a major or minor proportion based on the polyarylenesulphide. Such other resins may include polytetrafluoroethylene,polyimides and polysulphones. The resin phase may also include fillers,pigments, dyes, surface active additives, stabilizers, cross linkingagents, coating aids such as silica or titanium oxide powders, and basesto enhance bonding.

The solvent phase may include or comprise mixtures of aryl esters ofaryl alcohols, for example one or more of benzyl benzoate, benzylphthalate, benzyl iosphthalate, and benzyl terephthalate, and othermaterials acting as diluents or extenders or viscosity reducers for theactive solvent and having no non-solvent action such as to prevent theblend having the necessary plasticizer or solvent action for the resinphase as the case may be.

The solvent phase may also include co-solvents which whilst having nosignificant solvent action on their own enhance the solvent action ofthe benzyl benzoate.

The solvent phase may also include other solvents for polyphenylenesulphide and when the resin phase includes other resins, solvents forsuch other resins even if these are not solvents for polyphenylenesulphide though in this case they are preferably miscible with benzylbenzoate to form a single solvent phase.

The compositions of the invention may extend from solid particulatematerials containing polyphenylene sulphide plasticized by benzylbenzoate or solid workable bodies of polyphenylene sulphide plasticizedby benzyl benzoate to slurries of polyphenylene sulphide plasticized ornot by benzyl benzoate in liquid vehicles which contain benzyl benzoatethe benzyl benzoate either being in the polyphenylene sulphide or in theliquid vehicle or in both, to pastes of polyphenylene sulphideplasticized or not with benzyl benzoate suspended or dissolved in benzylbenzoate or benzyl benzoate containing vehicles or spreadable, dippableor sprayable solutions of polyphenylene sulphide in benzyl benzoate orbenzyl benzoate containing solvents.

The polyarylene sulphide resin that can be used in the present inventionmay be a polymer made by the method disclosed in U.S. Pat. No. 3,354,129but in general can be represented as a polymer including a recurringunit of the formula ##STR1## in which the ring A may be substituted.

One such form of substitution may be represented by the formula ##STR2##in which:

X represents a fluorine, chlorine, bromine or iodine atom, preferablychlorine or bromine, and Y represents a hydrogen atom, ##STR3## --S--R',--SO₃ H or --SO₃ M groups in which:

R represents a hydrogen atom, an alkyl, cycloalkyl, aryl, aralkyl, oralkaryl group containing 1 to 12 carbon atoms and in which:

M represents an alkali metal atom of a sodium or potassium atom and inwhich:

p is 0 to 4 and q is 2 to 4.

Polyphenylene sulphide in which the repeat unit can be represented bythe formula ##STR4## is preferred.

The polyarylene sulphides may be partially oxidized or may have abranched or cross linked structure though non-cross linked polymers orones having a low degree of cross linking and thus relatively low M.W.are preferred e.g. those having M.W.'s in the range 17,500 to 5000. Moregenerally polyarylene sulphides having melting points in the range of280° C. to 300° C. are preferred. Also materials having intrinsicviscosities in chloronapthalene at 260° C. of at least 0.1, e.g. 0.1 to0.3 especially 0.13 to 0.23 are preferred.

Polyphenylene sulphide has a solubility parameter of 8.5 to 9.5. UncuredPPS sold under the Trade Mark Ryton V1 has a melt flow index of 1000g/min. by the American Society Test Method (ASTM, D1238. Using the sametest, part cured PPS sold under the Trade Marks Ryton P2 and P3 havemelt flow indices of 300 and 125 g/min. respectively. In thosecompositions including PPS in particulate form the particle size may bein the range 10-200 microns and use of powder of such particle size isconvenient as a starting point for the preparation of single phasesystems in accordance with the invention.

The preferred solvent compounds for use in the present invention may berepresented by the formula ##STR5## where X, Y, W and Z represent ahydrogen atom or a halogen atom e.g. a chlorine atom.

The most preferred compound is Compound I, when X, Y, W and Z are allhydrogen. A less preferred compound is Compound I when W or Z is chlorieand X, Y and Z or W are hydrogen, namely benzyl monochlorobenzoate.

Benzyl benzoate has the following properties:

melting point 18°-20° C.

boiling point 320° C.

solubility parameter 9.3

Other solvent compounds which may be used in the present invention maycomprise phenyl benzoate, di-phenyl phthalate, di-benzyl ether, benzoicanhydride and di-phenyl sulphone.

According to a preferred aspect of the invention there is provided amethod of coating a bearing backing comprising mixing polyarylenesulphide with an aryl ester of an aryl alcohol, applying the mixture tothe backing, and subsequently evaporating the ester, and at least partlycuring the polyarylene sulphide simultaneously to leave the polyarylenesulphide in an at least partly cured state.

Preferably the polyarylene sulphide is polyphenylene sulphide andpreferably the ester is benzyl benzoate.

The resin and ester may both be in the solid state and thus may be inthe form of a powder mixture. Alternatively, the ester may be in theliquid state so that the mixture may be a paste or slurry of resin inthe ester or may be a solution of the resin in ester.

The components are preferably heated until they form one continuousliquid phase. The liquid may be cooled at this stage for example inorder to promote precipitation of the resin in the form of fine crystalsin the ester.

This step is not absolutely necessary in all cases but may beadvantageous for example if it is desired to store the formulation forany length of time.

Preferably the nature of the ester and the resin are such that when themixture is heated the resin and ester form a single phase and as theester evaporates, the resin undergoes curing. Preferably the ester doesnot evaporate completely until the resin is almost completely cured.Preferably a minimum of ester is employed since this may be lost inevaporation.

The method according to the invention may therefore render it possibleto produce a cured polyarylene sulphide in the form of a thin filmhaving a thickness hitherto thought to be unobtainable for example aslow as from 1 to 4×10⁻⁶ m, for example 3×10⁻⁶ m.

Various methods may be employed in applying the mixture prior to curing.In the case of a dry powder mixture this may be applied for example byelectrostatic spraying, dry powder spraying or by fluidised bed methods.In the case of a paste or wet powder this may be applied for example bywet spraying or spreading while in the case of slurries and solutionsthese may be applied by wet spraying or by painting or the article towhich the resin is to be applied may be dipped into the mixture.

The invention may be carried into practice in various ways and will beillustrated in the following specific examples. All percentages in thefollowing examples are by weight.

Examples 1 to 18 are examples of bearing blanks coated withpolyphenylene sulphide.

EXAMPLE 1

8% uncured polyphenylene sulphide sold under the Trade Mark Ryton V1 wasmixed with 92% benzyl benzoate. The mixture was heated to a temperaturein the range 250° to 290° C. by which time the polyphenylene sulphidehad dissolved in the benzyl benzoate. A cold bearing blank formed froman aluminium alloy including 6% tin or 11% silicone was immersed for 0.5seconds and withdrawn. A coating of solution had adhered to the blank.The coated blank was transferred to an air circulatory oven andmaintained at a temperature between 300° and 310° C. for five minutes.The temperature was then increased to a temperature between 370° to 380°C. for a further 15 minutes after which time the benzyl benzoate hadevaporated and the polyphenylene sulphide was fully cured. The layer ofpolyphenylene sulphide produced was approximately 0.001 cm in thickness.

EXAMPLE 2

30% uncured polyphenylene sulphide were dissolved in a solutioncomprising 10% diphenyl phthalate and 60% benzyl benzoate and held at atemperature between 250° 290° C. A bearing blank similar to that used inexample 1 was immersed in the solution for 2 minutes thus allowing theblank and solution to reach a thermal equilibrium. The blank, with anadherent coating of solution, was transferred to an oven and heated to atemperature between 300° and 310° C. for five minutes and then to atemperature between 370° and 380° C. for a further 15 minutes. A coatingsimilar to that obtained in example 1 was obtained.

EXAMPLE 3

A suspension of uncured polyphenylene sulphide was prepared by mixing30% polyphenylene sulphide with 10% diphenyl phthalate and 60% benzylbenzoate, heating the mixture to a temperature between 250° and 290° C.in order to dissolve the polyphenylene sulphide, and subsequentlycooling the solution to a room temperature while maintaining a vigorousagitation. A fine cloudy gelatinous suspension of polyphenylene sulphidewas thus formed. The suspension was sprayed on to two bearing blanks ofan aluminium alloy containing 6% tin or 11% silicone, one of which wasat room temperature and the other of which was heated to about 250° C.The sprayed blanks were transferred to an oven where they were held at atemperature between 300° and 310° C. for five minutes and then held at atemperature between 370° and 380° C. for a further 15 minutes. Anadherent coating of polyphenylene sulphide 0.001 cm thick was producedon each blank.

EXAMPLE 4

A water-based slurry was produced by ball milling together for 24 hours30% uncured polyphenylene sulphide, 49% unsaturated calcium hydroxidesolution, 1% of a nonionic surfactant (as sold under the Trade MarkTriton X 100)20% diphenyl sulphone. This slurry was used to spray coattwo blanks as described in example 3 above and similar coatings wereobtained.

EXAMPLE 5

A bearing blank of an aluminium alloy including 6% tin or 11% silicone,at room temperature, was sprayed with a solution comprising 10% phenylbenzoate in 90% benzyl benzoate until the surface sprayed was fully wetbut not dripping. The wetted surface was sprayed electrostatically witha powder mixture of 99% polyphenylene sulphide and 1% calcium hydroxide.The blank was placed in an oven and heated to a temperature of between300° and 310° C. for 5 minutes followed by being heated to a temperaturebetween 370° and 380° C. for a further 15 minutes. As in the previousexamples a satisfactory thin coating was obtained.

EXAMPLE 6

This was carried out in the same way as example 5 but with diphenylphthalate replacing phenyl benzoate. Similar results were obtained asthose of example 5.

EXAMPLE 7

This was carried out in the same was as example 4 but the calciumhydroxide solution was replaced with an aqueous suspension ofpolytetrafluoroethylene comprising between 15 and 30%polytetrafluoroethylene. Similar results were obtained to those ofexample 4.

EXAMPLE 8

The following ingredients were mixed intimately in a high speed mixer:70% uncured polyphenylene sulphide, 20% diphenyl sulphone, 9% diphenylphthalate and 1% calcium hydroxide. The mixture was electrostaticallysprayed on to a bearing blank of an aluminium alloy including 6% tin or11% silicone, at room temperature. The blank was placed in an oven whereit was heated to a temperature between 300° and 310° C., held at thattemperature for 5 minutes and subsequently raised to a temperaturebetween 370° and 380° C. for 15 minutes. An adherent coating ofpolyphenylene sulphide was obtained having a thickness of 0.001 cmapproximately.

EXAMPLE 9

This was carried out in the same was as example 8 except that the blankwas at a temperature between 350° and 370° C. prior to its being sprayedwith the mixture. Similar results were obtained to those of example 8.

EXAMPLE 10

This was carried out in the same way as example 1 but with the uncuredpolyphenylene sulphide replaced by 99% part cured polyphenylene sulphide(sold under the Trade Mark Ryton P2) and 1% calcium hydroxide powder.Similar results were obtained to those obtained in example 1 but it wasfound that the curing time was shorter than in example 1.

EXAMPLE 11

This was carried out in the same way as example 2 but an uncuredpolyphenylene sulphide was replaced by a mixture of 99% part curedpolyphenylene sulphide and 1% calcium hydroxide, and the diphenylphthalate/benzyl benzoate mixture was replaced by benzyl benzoate alone.Similar results were obtained to those of example 2 but it was foundthat the curing time was shorter than in example 2.

EXAMPLE 12

This was carried out in the same way as example 3 but the uncuredpolyphenylene sulphide was replaced by a mixture of 99% part curedpolyphenylene sulphide and 1% calcium hydroxide, and the diphenylphthallate/benzyl benzoate mixture was replaced by benzyl benzoatealone. Similar results were obtained to those in example 3 but it wasfound that the curing time was shorter than in example 3.

EXAMPLE 13

This was carried out in the same way as example 4 but the uncuredpolyphenylene sulphide was replaced entirely by part cured polyphenylenesulphide. Similar results were obtained to those obtained in example 4but it was found that the curing time was shorter than in example 4.

EXAMPLE 14

This was carried out in the same way as example 5 but the uncuredpolyphenylene sulphide was replaced entirely by part cured polyphenylenesulphide. Similar results were obtained to those obtained in example 5but it was found that the curing time was shorter than in example 5.

EXAMPLE 15

This was carried out in the same way as example 6 but the uncuredpolyphenylene sulphide was replaced entirely by part cured polyphenylenesulphide. Similar results were obtained to those obtained in example 6but it was found that the curing time was shorter than in example 6.

EXAMPLE 16

This was carried out in the same way as example 7 but the uncuredpolyphenylene sulphide was replaced by a mixture of 99% part curedpolyphenylene sulphide and 1% calcium hydroxide. Similar results wereobtained to those obtained in example 7 but it was found that the curingtime was shorter than in example 7.

EXAMPLE 17

This was carried out in the same way as example 8 but the uncuredpolyphenylene sulphide was replaced entirely by part cured polyphenylenesulphide. Similar results were obtained to those obtained in example 8but it was found that the curing time was shorter than in example 8.

EXAMPLE 18

This was carried out in the same way as example 9 but the uncuredpolyphenylene sulphide was replaced entirely by part cured polyphenylenesulphide. Similar results were obtained to those obtained in example 9but it was found that the curing time was shorter than in example 9.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A method of applying a coating of polyarylenesulphide to a bearing which comprises:applying a mixture of polyarylenesulphide and an aryl ester of an aryl alcohol to the surface of abearing blank; and subsequently heating said mixture to evaporate saidester and to cure said coating.
 2. A method according to claim 1 whereinsaid polyarylene sulphide is polyphenylene sulphide.
 3. A methodaccording to claim 1 wherein said ester is benzyl benzoate.
 4. A methodaccording to claim 1 wherein said mixture is a dry powder mixture.
 5. Amethod according to claim 1 wherein said mixture is in the form of apaste.
 6. A method according to claim 1 wherein said polyarylenesulphide is in suspension in said ester; said ester being in the liquidphase.
 7. A method according to claim 1 wherein said polyarylenesulphide is dissolved in said ester.
 8. A method according to claim 1wherein said ester is in solid solution in said polyarylene sulphide.